sla: remove redundant locking.

sla.lock was already locked in the only place that sla_check_reload() was called.
Remove the redundant locking of sla.lock done in this function.  Less recursive
locking is A Good Thing.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@386190 65c4cc65-6c06-0410-ace0-fbb531ad65f3